15.3. Constructing, Setting, and Using Colors

Problem

You want to be able to obtain references to color
objects in order to use them while you are drawing various forms on a
view, such as text, rectangles, triangles and line segments.

Solution

Use the UIColor class.

Discussion

UIKit provides programmers with a high-level abstraction of
colors, encapsulated in the UIColor
object. This class has a few really handy class methods such as
redColor, blueColor, brownColor, and yellowColor. However, if the color you are
looking for isn’t one of the explicitly
named UIColor methods, you can
always use the colorWithRed:green:blue:alpha: class
method of UIColor class to load
the color that you are looking for. The return value of this class
method is a value of type UIColor.
The parameters of this method are:

red

The amount of red to use in the color. This value can be
anything between 0.0f to
1.0f, where 0.0f omits all red and 1.0f makes the red component as dark
as possible.

green

The amount of green to mix with the red in the color. This
value also ranges from 0.0f
to 1.0f.

blue

The amount of blue to mix with the red and green in the
color. This value also ranges from 0.0f to 1.0f.

alpha

The opaqueness of the color. This value can range from
0.0f to 1.0f, with 1.0f making the color completely
opaque and 0.0f making the
color completely transparent (in other words, invisible).

After you have an object of type UIColor, you can use its set instance method to make the current graphics context use that color ...

The best content for your career. Discover unlimited learning
on demand for around $1/day.